The present invention relates to a color changing apparatus for multiple color electrostatic coating which is performed with a conductive coating material such as an aqueous coating material using an electrostatic coating spray gun supplied with a high voltage. More specifically, the present invention relates to a color changing apparatus for multiple color electrostatic coating of conductive coating material, for realizing easy maintenance of a system other than the system which is being used for coating without being influenced by a high voltage applied and for facilitating color changing.
An electrostatic coating method is a technique for applying a high voltage (generally, 80 to 125 kV) to a corona pin provided in a coating material spray gun and electrostatically charging the coating material which is sprayed from the spray gun to a high potential so as to apply the coating material on a surface of a subject of coating which is grounded. Accordingly, when a conductive coating material based on a conductive solvent such as water, methanol or the like is used, a conductive path is formed by the conductive coating material from the spray gun to a coating tank through a coating material supply line. The coating material supply system including the coating material tank and a pump needs to be insulated from the ground since otherwise the high voltage is grounded through the coating material supply line and thus cannot be applied to the corona pin provided on the spray gun.
In such an apparatus, high potential electrostatic charges are accumulated in all the devices from the spray gun and the coating material supply system. It is very dangerous if the operator inadvertently contacts a device in the coating material supply system having such a large discharge energy accumulated therein. Therefore, the coating material cannot even be supplemented to the coating material tank while the apparatus is in operation. In the case where a color changing apparatus for multiple color coating has a structure in which a plurality of coating material supply systems respectively for multiple colors are directly connected to one another through a switching valve or the like, electrostatic charges are accumulated, through a switching valve, even in a coating material supply system for a color other than the color which is in use. Thus, the degree of danger is increased, and the coating material cannot be supplemented even to a coating material tank for a color other than the color which is in use.
As a method for alleviating these problems regarding color changing for multiple color coating, technologies described. In Japanese Laid-Open Publication Nos. 4-200663 and 4-200664 are proposed. The technology disclosed in Japanese Laid-Open Publication Nos. 4-200663 will be first described. An electrostatic coating apparatus for conductive coating material which is used for applying a conductive coating material by an electrostatic coating machine supplied with a high voltage is disclosed. A plurality of pumps are provided in an electrically insulating state, the plurality of pumps having a coating material inflow opening and a coating material outflow opening through which a required amount of conductive coating material introduced through the coating material inflow opening is pushed out by pressure at a prescribed flow rate in accordance with the coating material discharge amount of the electrostatic coating machine. Detachably connected to the coating material inflow opening of each of the pumps is a coating material supply pipe, which is connected to a respective color changing valve apparatus including a cleaning air supply valve and a cleaning liquid supply valve. The coating material outflow opening of each pump is connected to a switching valve for communicating the coating material outflow opening to an outflow path on the electrostatic coating machine side or to an outflow path on the exhaust liquid tank side. Each exhaust liquid pipe connected to the exhaust liquid tank is detachably connected to the outflow path on the exhaust liquid tank side.
The technology disclosed in Japanese Laid-Open Publication Nos. 4-200664 will be described. An electrostatic coating apparatus for conductive coating material which is used for coating a conductive coating material by an electrostatic coating machine supplied with a high voltage is disclosed. A plurality of coating material pressure-supply tanks for pushing out a required amount of conductive coatings material stored therein by air pressure and supplying a constant amount of the conductive coating material to the electrostatic coating machine, and a cleaning liquid pressure-supply tank for pushing out a required amount of cleaning liquid stored therein by air pressure and supplying the cleaning liquid to the electrostatic coating machine are provided in an electrically insulating manner. The coating material pressure-supply tanks and the cleaning liquid pressure-supply tank are connected to the respective color chancing valves provided in parallel to a manifold communicated to the electrostatic coating machine. The coating material pressure-supply tanks are each provided with a coating material supplement opening, and the cleaning liquid pressure-supply tank is provided with a cleaning liquid supplement opening. The coating material supplement opening is detachably connected to a supply pipe for supplying a conductive coating material of a corresponding color, and the cleaning liquid supplement opening is detachably connected to a cleaning liquid supply pipe.
The above-described conventional technologies, i.e., the technologies disclosed in Japanese Laid-Open Publication Nos. 4-200663 and 4-200664 have the following problems. The technology disclosed in Japanese Laid-Open Publication No. 4-200663 has the problems that the circuit is relatively complicated and accordingly the operation is relatively troublesome; and each coating material supply system requires two separate mechanisms of a coating material supply system and an exhausted liquid system. The technology further has the following problem. Although not clear from the publication or the figures, a conductive path is formed, through the conductive coating material, in a plurality of coating material supply systems (i.e., pumps, coating material tanks and the like) respectively connected to color clanging valves (CV1 through CV3) of color changing valve devices (9A, 9B, 9C) while the systems are in use (i.e., connected to the electrostatic coating machine). Therefore, none of the color coating materials can be supplemented due to the possible danger of high potentials. Therefore, before supplementing the coating materials, the coating operation needs to be stopped so as to shield the high voltage.
The technology disclosed in Japanese Laid-Open Publication No. 4-200664 also has the following problem. A conductive path is formed, through the conductive coating material or the cleaning liquid, even in a plurality of coating material pressure-supply systems (1A, 2B, 2C) and the cleaning liquid pressure-supply tank (3) while coating is performed. Therefore, none of the color coating materials can be supplemented due to the possible danger of high potentials. Therefore, before supplementing the coating materials, the coating operation needs to be stopped so as to shield the high voltage.
The present invention made in light of the above-described problems has an objective of providing a color changing apparatus for multiple color electrostatic coating of conductive coating material, which has a relatively simple structure and realizes a relatively simple operation; which separates coating material supply systems other than the system for the color which is being used for coating from a circuit charged with a high voltage, so as to avoid any influence of the high voltage, so that works such as coating material supplement and maintenance can be done while the coating is performed; and which realizes easy color changing.
In order to solve the above-described problems, the present invention provides the following method. In a color changing apparatus for multiple color electrostatic coating of conductive coating material, a pipe joint provided to be movable on a guide rail and an electrostatic spray gun connected to the pipe joint a through a pipeline are provided. A plurality of coating material supply circulation circuits, including a liquid tank, a pump and a pipe joint b disengageably engageable with the pipe joint a are provided. The liquid tank, the pump and the pipe joint b are connected through a pipeline. The pipe joint a and the pipe joint b in the plurality of coating material supply circulation circuits can be selectively disengaged.